Pic. 279. Removal and installation of rear brake pads: 1 - rear axle; 2 - holding spring; 3 - external brake shoe; 4 - internal brake shoe; 5 - brake cylinder; 6 - wire of the pad wear sensor; 7 - plug; 8 - guide pin
The pads should be replaced if the pads are worn to a thickness of less than 2 mm. You can check this by removing the wheel with the caliper installed, as described in subsection 12.3.1. When replacing, refer to Fig. 279. On mod. 412D calipers with two pistons. Brake pads must be replaced in the following order:
- unscrew the cap of the brake fluid reservoir;
- press the brake pedal several times to remove the vacuum in the system. Place the car on supports at the rear and remove the rear wheels;
Pic. 280. Disconnecting the wear sensor wire
- Disconnect the pad wear sensor wire as shown in fig. 280;
- using a screwdriver and pliers, remove both locking clips from the pins of the brake pads 4 (see fig. 279);
- pry off the ends of the spring 2 with a screwdriver and remove it;
Pic. 281. Loosening the brake caliper mounting bolts
- on the reverse side of the caliper with a screwdriver, pry off both plugs of the mounting bolts shown in Fig. 281, and unscrew the bolts with a hexagon. After loosening the bolts, remove the caliper cylinder. Hang the cylinder on a wire to the front axle so that it does not hang on the brake hose. Remove the block from the removed cylinder;
- remove the second pad from the caliper bracket;
- thoroughly clean the receiving slots of the caliper and check that the mudguards and cylinder are not damaged;
Pic. 275. Recessing the piston of the brake caliper before installing the pads
- if the pads are worn very badly, it will be necessary to sink the piston into the brake cylinder, as shown in fig. 275. To do this, you can also install the inner shoe on the piston and slowly press it inward. At the same time, make sure that brake fluid does not leak from the reservoir. Pump out some liquid if necessary.
When installing the pads, you must perform the following operations:
- clean the contact surface under the brake pads in the caliper;
- pump out some brake fluid from the master cylinder reservoir as described above;
- sink the piston into the cylinder. For this, a clamp is used, shown in Fig. 275;
Pic. 276. Inner shoe
- install the shoe with the spring in the caliper cylinder, as shown in fig. 276, and press in the direction of the arrow;
Pic. 273. Outer shoe
- insert the outer pad into the mounting points of the caliper bracket so that it occupies the position shown in fig. 273;
Pic. 282. Installing the outer shoe on the bracket
- insert the second pad into the caliper bracket. At the same time, position its outer side as shown in Fig. 282;
Pic. 277. Tightening the caliper mounting bolts
- carefully place the cylinder body over the pads and screw the mounting bolts through the pads into the caliper bracket. Wrap them with a hexagon, as shown in fig. 277, torque 25–28 Nm;
- after tightening the bolts, put plugs on them;
Pic. 283. Installing the retaining spring
- install the spring in the caliper and bracket. Check for correct spring installation (pic. 283);
- twist the wear sensor wire into a spiral and connect to the contact of the caliper;
- press the brake pedal hard several times so that the pads approach the disc;
- if necessary, add brake fluid to the reservoir;
- install the wheels, lower the car and tighten the wheel bolts to a torque of 160–180 N·m;
- after installation, press the brake pedal several times until its normal travel is established. If this is not done, the brakes may not work when the vehicle is moving for the first time. If the pedal «fails», check the tightness of the system. During the first trips after installing new pads, do not brake too hard. In order for the brakes to work well, you should brake several times with a smooth pressure on the pedal from a speed of 80 km / h to 40 km / h. After each braking, you must wait so that the brakes do not overheat.
Recommendations for the use of brake pads
If the pads are too worn, check that the pistons of both brake calipers move normally. Otherwise, it is recommended to check the operation of the brackets at the service station. Pads should be replaced when pads are worn to a thickness of 2.0 mm or less. Oily or grease-stained pads should also be replaced. Use only genuine Mercedes-Benz pads and replace only as a set. If the pads are worn down to metal, the brake disc may have been damaged. This, of course, must be avoided under any circumstances.
Brake discs with traces of friction lining material should be thoroughly cleaned before installing new pads. New pads should be worn in. To do this, while gently pressing the brake pedal, brake several times from a speed of 80 km/h to 40 km/h. After each braking, you need to pause so that the brakes do not overheat. Before running in the pads, it is important to avoid emergency braking.